What are the functions and properties of a ligand protein receptor?
A protein receptor on the surface of the cell binds to a ligand and causes a change within the cell
The receptor protein hangs out on the surface of the cell membrane and binds to a ligand. When the ligand binds to the receptor a change occurs. The ligand is the first messenger, and the receptor then causes a change in the cell. It is lodged in one or more membranes, has an active site to bind to something specifically, and may have a domain underneath it or something else underneath it to start spreading a change in the cell
The receptor can start a process or stop a process in the cell by directly contacting other molecules, second messengers that spreading the message across the cell and causing a change.
The receptor could have sub units beneath it that activate when the ligand attaches: they pop off and start a process. Some receptors have recruitment stations (docking stations) where things attach (and, for example, get phosphorylated when the ligand binds).
A good example is when a macrophage sends a ligand to bind to the tumor necrosis factor receptor . This starts changes in the cell that results in caspases activating each other: a proteolytic cascade. One caspase cleaves and activates another til the executioner caspase is activated and kills the cell . This is the TLDR version of it but it all starts with the receptor.